USDA Reports Reveal Biosecurity Risks at H5N1-Affected Dairy Farms

Jun 14, 2024

By Lisa Schnirring 

Shared equipment and shared personnel working on multiple dairy farms are some of the main risk factors for ongoing spread of highly pathogenic H5N1 avian flu in dairy cows, the US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) said today in a pair of new epidemiologic reports.

One of the reports is an overview based on the results of questionnaires from affected dairy herds, and the other is a deep dive into the dairy cow and poultry outbreaks in Michigan, the state hit hardest by outbreaks in dairy cows, which now number at least 94.

At a media briefing today, Kammy Johnson, DVM, PhD, a veterinary epidemiologist with APHIS, said the multistate epi report provides a national clinical picture of the disease in cows and the routes of spread, and the report from Michigan is an early snapshot showing what's happening in the field.

Both suggest three key factors for transmission between farms: shared equipment and vehicles, shared personnel who may inadvertently carry the virus between farms on their clothes or boots, and animal movements. "The bigger picture is that enhanced biosecurity is really critical," she said.

So far, genomic evidence continues to suggest a single introduction from wild birds, with further spread among dairy farms, such as from Texas to Michigan in the initial weeks of the outbreak. Now the virus is spreading between farms owing to multiple direct and indirect factors, according to the APHIS reports.

Multiple factors fuel spread between farms

Questionnaires revealed that more than 20% of farms received cattle within 30 days of clinical signs, and 60% of farms continued to move cattle off the facilities after animals showed signs of illness.

Most farms had cats present, and more than 50% of those had sick or dead cats. Also, more than 20% of dairy farms also had chickens or poultry, nearly all of which had sick or dead birds. USDA officials said cats are the canary in the coalmine, but cats and other animals, such as wild birds, probably aren't playing a major role in the spread of the virus, though they could serve as fomites.

Clinically, lactating cows are the most affected, with signs of illness in less than 10% of herds and mortality and culling averaging less than 2%.

Meanwhile, the report from Michigan is based on data gathered by an APHIS strike team that the Michigan Department of Agriculture and Rural Development invited into the state to probe links between infected dairy farms and spillovers into poultry premises. It includes findings from 15 dairy farms and 8 poultry producers. 

About 20% of dairy workers, and some of their family members, worked on multiple dairy farms. About 7% of workers on affected dairy farms also worked on poultry farms. Regarding equipment, about 62% of farms shared vehicles to transport cattle, and only 12% cleaned the vehicles before use.

The farms also had frequent visitors, such as veterinarians, feed consultants, and contract haulers. Nearly all of the affected farms are part of the same dairy co-op, and the diaries all used the same deadstock hauler.

So far, the B3.13 outbreak strain has not been found in Michigan's migratory waterfowl.

The authors of the report praised the willingness of Michigan's dairy producers to participate in the investigation, emphasizing that the findings have greatly increased the body of knowledge about B3.13, both in Michigan and nationally. "This report could not have been completed without them."

Lingering questions about newly affected states, outbreak scope

At today's briefing, Johnson said it's too early to assess how H5N1 spread to the three more recently affected states: Iowa, Minnesota, and Wyoming. She added that today's report paints a national picture of what's known about the outbreaks so far and adds some useful context to understanding the events.

She said the findings are a solemn reminder that farms already have tools for managing the spread of the virus. "Biosecurity is the key to prevention."

Mark Lyons, DVM, who directs the Veterinary Services Ruminant Health Center at APHIS, said it's still not clear if the outbreaks are still gaining steam and that animal health officials are still trying to understand the full scope of the situation, though they expect to find additional cases.

As of yesterday, the APHIS total was at 94 dairy farm outbreaks in 12 states. Yesterday, the Iowa Department of Agriculture and Land Stewardship reported the state's third outbreak in a dairy herd, which affected a second location in Sioux County.

Updates on human investigations, vaccine production

Responding to questions about Michigan's second case-patient in a dairy worker, who, unlike the other previous patients, had respiratory symptoms, Nirav Shah, JD, MD, principal deputy director for the Centers for Disease Control and Prevention (CDC), said the polymerase chain reaction cycle threshold  (Ct) value for the patient's sample was high, suggesting a lower amount of viral RNA in the sample. 

The situation made it difficult for CDC scientists to generate a full genomic sequence, though they were able to piece together a large portion of it, he said.

So far, the findings are reassuring, with no changes to suggest that the virus that infected the patient has a higher ability to transmit and no changes in the neuraminidase that would suggest reduced sensitivity to H5 vaccines or existing therapies, Shah said.

Regarding vaccines, David Boucher, PhD, director of infectious disease preparedness and response at the Department of Health and Human Services Administration for Strategic Preparedness, said federal health officials are still on track to produce 4.8 million vaccine doses from bulk antigen on a 3- to 4-month timeline, with manufacturing starting in the middle of July. 

In other H5N1 developments:

  • Minnesota reported another H5N1 outbreak in poultry, part of ongoing sporadic detections. The virus struck a commercial turkey farm that has 92,400 birds in Lyon County, located in the southwestern part of the state, according to the latest APHIS update.
  • The Minnesota Board of Animal Health today announced an H5N1 testing requirement for lactating dairy cattle that will be brought to exhibits. The measure takes effect on June 18 and lasts until the end of 2024, unless the order is extended or rescinded before then.
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